1. Field of the Invention
The present invention relates to a process for forming a polymeric solution or gel having a viscosity of at least about 50,000 cps which includes the steps of dissolving an amine neutralized sulfonated polymer in a solvent to form a polymeric solution, a concentration of the amine neutralized sulfonated polymer in the solution being about 0.1 to about 20 wt. %, a viscosity of the solution being less than about 20,000 cps; and adding about 1 to about 500 vol. % of inorganic base solution to the polymeric solution having a viscosity less than about 20,000 cps, the water of the inorganic base solution being immiscible with the solvent and the polymeric solution, the viscosity of said polymeric solution increasing rapidly upon the addition of said inorganic base solution from less than 20,000 cps to greater than 50,000 cps.
2. Description of the Prior Art
There are many applications for very viscous or gelled solutions of polymers in organic liquids which are quite diverse. There are also a number of physical and chemical techniques for preparing such systems. The present invention is concerned with a process for converting a relatively low viscosity organic liquid solution of an ionic polymer into a very viscous or gelled system via a rapid process which under certain conditions can be reversed. The potential applications for this process and the products derived therefrom will be evident in the instant application.
There are major problems in the direct preparation of viscous polymer solutions or gels via conventional techniques such as polymer dissolution. For example, attempts to form a high viscosity (&gt;500,000 cps) solution of polystyrene in a suitable solvent such as xylene can be difficult. The levels of polymer required are either very high (20 to 50 wt. % concentration) or the molecular weight of the polymer must be extremely high. In either event the dissolution process is extremely slow even at elevated temperatures, and even then it is difficult to achieve homogeneous polymer solutions free of local concentrations of undissolved, or poorly dissolved polymer. Thus, the process of achieving such solutions can be difficult and the concentration of polymer in the solution to achieve high viscosities can be uneconomically high.
These are various chemical approaches to the solution of the problems outlined above, that is polymer chain lengthening reactions which can occur to give viscous solutions such as by the reaction of hydroxyl terminated polymers with diisocyanates etc. Such processes have inherent disadvantages which preclude their use in the intended applications of this invention.
The instant invention describes a process which permits (1) the preparation of polymer solutions of sulfonated polymers in organic liquid having reasonably low viscosities (i.e., less than about 20,000 cps), (2) the preparation of extremely viscous solutions or gels from such solutions by the simple process of mixing a suitable basic solution with the polymer solution and (3) the reversion of such viscous solutions or gels to relatively low viscosity mixtures by the reincorporation of polar cosolvents which are water immiscible at a desired stage. These operations are achieved by the use of the appropriate concentration of polymers having low concentrations of ionic groups present, preferably metal sulfonate groups. Such polymers are described in detail in a number of U.S. patents (U.S. Pat. Nos. 3,836,511; 3,870,841; 3,847,854; 3,642,728; 3,921,021) which are herein incorporated by reference. These polymers possess unusual solution characteristics some of which are described in U.S. Pat. No. 3,931,021. Specifically such polymers such as lightly sulfonated polystyrene containing about 2 mole % sodium sulfonate pendant to the aromatic groups are typically not soluble in solvents commonly employed for polystyrene itself. However, the instant invention describes a select class of amine neutralized sulfonated polymers which readily dissolve in selected solvents. The sulfonate groups of the sulfonated polymers are neutralized with a secondary or tertiary amine having at least 6 carbon atoms.
The remarkable and surprizing discovery of the instant invention pertains to the following observation.
When small (or large) amounts of base are combined and mixed with solutions of the critically selected ionic polymers dissolved in the solvent as those described above, it is possible to convert such low viscosity systems into extremely viscous gels or solutions. Indeed it is possible to achieve increases in viscosity by factors of 10.sup.4 (10,000) or more by the addition of only 5 to 15% water based on the polymer solution volume.
This unusual behavior is postulated to arise from the reaction of the aqueous base with the amine neutralized sulfonated polymer and the consequent development of stronger ionic associations. Consequently, when this occurs the physical crosslinking of the ionic groups is again manifested resulting in a tremendous increase in solution viscosity. The resulting gels or thick solutions appear quite homogeneous.